An organic EL element is an element which has a configuration in which a thin film containing a fluorescent organic compound is held between a cathode and an anode. In the organic EL element, electrons and holes are injected from the respective electrodes into the thin film to generate excitons through the recombimation of the electrons and holes. The organic EL element produces luminescence by utilizing emission of light (fluorescence or phosphorescence) at the deactivation of the excitons.
The features of the organic EL element is that it is possible to obtain a high intensity surface luminescence on the order of 100 to 100,000 cd/m2 at a low voltage of less than 10V, and that it is possible to produce luminescence of from blue to red by the selection of the kind of fluorescent material.
The organic EL element is drawing attraction as a device for realizing a large area full color display element at a low cost (see, Institute of Electronics, Information and Communication Engineers (IEICE) Technical Report Vol. 89, No. 106, 1989, p. 49). According to the report, bright luminescence of blue, green and red were obtained by forming a luminescent layer using an organic luminescent material which emits strong fluorescence. This fact is considered to mean that it is possible to realize a high brightness full color display by using an organic coloring matter which emits strong fluorescence in a thin film state and has less pin hole defects.
In addition, in Japanese Laid-Open Publication No. Hei 5-78655, there is proposed to use an organic luminescent layer containing a luminescent material which is formed of a mixture of an organic charging material and an organic luminescent material, thereby obtaining a high brightness full color element by preventing quenching due to higher concentration as well as expanding the latitude in the selection of the luminescent material.
Further, in Appl. Phys. Lett. Vol. 64, 1994, p. 815, it is reported that a white luminescence was obtained by using polyvinyl carbazole (PVK) as a luminescent material and doping it with coloring matters corresponding to three primary colors R, G and B. However, in neither of the above references, the configuration or the method of manufacture of an actual full color display panel is not shown.
In the organic thin film EL elements using the organic luminescent materials described above, in order to realize a full color display device, it is necessary to arrange organic luminescent layers which emit any one of the three primary colors for the respective pixels. However, there is a problem in that a polymer or precursor that forms the organic luminescent layer lacks a sufficient resistance to a patterning process such as photolithography, so that it is very difficult to carry out patterning with highly precision.
Further, when several organic layers are to be formed by a vacuum deposition method, it takes a long time. Therefore, such a method cannot be said to be an efficient method of manufacturing the element.